FIELD
[0001] The present disclosure generally relates to audio amplifiers, and more particularly,
to fully-differential programmable gain amplifiers and a high efficiency audio amplifier
systems and processes.
BACKGROUND
[0002] FIG. 1A is a circuit diagram of a prior art differential programmable gain amplifier
100 with input
101. The differential gain amplifier
100 includes a multiplying digital to analog converter (DAC)
102, first current-to-voltage converter
107, second current-to-voltage converter
108, first differential amplifier
109 and second differential amplifier
110. The input signal of differential programmable gain amplifier
100 is received by input
101. Current-to-voltage converters
107 and
108 translate the portion of the input current remaining after passing through DAC
102 into a voltage signal. The voltage signal from the outputs of current-to-voltage
converters
107 and
108 are applied to inputs of the first differential amplifier
109 and the second differential amplifier
110. First differential amplifier
109 and the second differential amplifier
110 sense the voltage between outputs of current-to-voltage converters
107 and
108 and produce differential output on outputs
115 and
120. However, this configuration requires an undesirably high number of components and
high tolerances. In order for differential gain amplifier
100 to operate efficiently, components of differential gain amplifier
100 must be matched. By way of example, differential gain amplifier
100 requires matching of components, such as current-to-voltage converters
107 and
108. In addition, differential gain amplifier
100 requires four operational amplifiers to produce the differential output. There is
a desire for a differential amplifier circuit that does not require high tolerances
of the components in differential amplifiers nor so many amplifying circuits in the
signal path. There is also a desire for a differential amplifier that maintains a
high common-mode rejection ratio, low control signal interference and low signal distortion.
[0003] FIG. 1B shows an exemplary output spectrum
150 for differential programmable gain amplifier
100 with a symmetrical drive. Differential programmable gain amplifier
100 compensates distortion caused by nonlinearity of MOSFET switches of DAC
102. Resistance of a closed MOSFET switch is a function of applied voltage. Full distortion
compensation takes place when the signals on inputs have equal amplitude and opposite
phase. By way of example, an input signal, such as a pure 1kHz sine wave, having signals
on input
101 with equal amplitude and opposite phase will generate spectrum
150 having with peak
155.
[0004] FIG. 1C shows an exemplary output spectrum
160 for differential programmable gain amplifier
100 with asymmetrical drive. For example, an input signal having a pure 1kHz sine wave,
with the input signal applied to a single input terminal or input
102 and second input signal terminal shorted to ground, will generate output spectrum
160 having peak
165 and second order distortion shown by peak
166. Differential programmable gain amplifier
100 does compensated second order distortion.
BRIEF SUMMARY OF THE EMBODIMENTS
[0005] Disclosed and claimed herein are a device and methods for amplifying a differential
signal. One embodiment is directed to a fully-differential programmable gain amplifier
including a first input, a second input, a first output, a second output, and a programmable
gain module coupled to the first input and the second input. According to one embodiment,
the programmable gain module includes a data latch circuit configured to control the
first set of switches for the first resistive ladder network to provide output to
the first current mode output, and control the second set of switches for the first
resistive ladder network to provide output to the second current mode output. According
to one embodiment, fully-differential programmable gain amplifier includes an amplifier
coupled to the first current mode output, the second current mode output, and the
data latch circuit, the amplifier configured to apply common mode voltage to the data
latch circuit. According to one embodiment, fully-differential programmable gain amplifier
includes a current-to-voltage converter coupled to the first current mode output,
the second current mode output, the first output and the second output. In one embodiment,
the current-to-voltage converter is configured to receive at least one output current
mode signal from the first current mode output and the second current mode output,
and produce an output signal by converting differential input received from the at
least one output current mode signal from the first current mode output and the second
current mode output.
[0006] In one embodiment, the programmable gain module is a dual multiplying digital to
analog converter.
[0007] In one embodiment, the programmable gain module includes a first resistive ladder
network coupled to the first input, a first set of switches for the first resistive
ladder network, the first set of switches coupled to a first current mode output,
a second resistive ladder network coupled to the second input, and a second set of
switches for the first second ladder network, the second set of switches coupled to
a second current mode output. According to one embodiment, the data latch circuit
is configured to control the first set of switches for the first resistive ladder
network to provide output to the first current mode output, and control the second
set of switches for the first resistive ladder network to provide output to the second
current mode output.
[0008] In one embodiment, the programmable gain module receives control signals to adjust
amplification of at least one signal received relative to the first input first and
second input signals.
[0009] In one embodiment, the amplifier is a voltage follower with the positive input connected
to a voltage ladder between the first current mode output and second current mode
output, the negative input connected to an output of the voltage follower by a negative
feedback loop and a floating ground supply of the programmable gain module.
[0010] In one embodiment, the amplifier is a correction module configured to sense a common-mode
signal between first current mode output and second current mode output and to provide
corrective feedback to the programmable gain module.
[0011] In one embodiment, the current-to-voltage converter is differential module configured
to produce a positive output signal to the first output and a negative output signal
to the second output, wherein the first output and second output are opposite each
other and equal in magnitude to the difference between the amplified first and second
input signals.
[0012] In one embodiment, the current-to-voltage converter includes a first output feedback
loop coupled to the first output and an input of the current-to-voltage converter,
and a second output feedback loop coupled to the first output and an input of the
current-to-voltage converter.
[0013] In one embodiment, the fully-differential programmable gain amplifier includes a
floating supply to power the programmable gain module.
[0014] In one embodiment, the fully-differential programmable gain amplifier includes a
galvanic isolator coupled to the programmable gain module, the galvanic isolator configured
to block low voltage DC current to the programmable gain module.
[0015] Another embodiment is direct to a fully-differential programmable gain amplifier
including a first input, a second input, a first output, a second output and a programmable
gain module coupled to the first input and the second input. The programmable gain
module including a first resistive ladder network coupled to the first input, a first
set of switches for the first resistive ladder network, the first set of switches
coupled to a first current mode output, a second resistive ladder network coupled
to the second input, a second set of switches for the first second ladder network,
the second set of switches coupled to a second current mode output, and a data latch
circuit. The data latch circuit configured to control the first set of switches for
the first resistive ladder network to provide output to the first current mode output,
and control the second set of switches for the first resistive ladder network to provide
output to the second current mode output. The fully-differential programmable gain
amplifier including an amplifier coupled to the first current mode output, the second
current mode output, and the data latch circuit, the amplifier configured to apply
common mode voltage to the data latch circuit. The fully-differential programmable
gain amplifier including a current-to-voltage converter coupled to the first current
mode output, the second current mode output, the first output and the second output,
the current-to-voltage converter configured to receive at least one output current
mode signal from the first current mode output and the second current mode output,
and produce an output signal by converting differential input received from the at
least one output current mode signal from the first current mode output and the second
current mode output.
[0016] Another embodiment is directed to a method for fully-differential programmable gain
amplifying. In one embodiment the method includes receiving, by a programmable gain
module of a fully-differential programmable gain amplifier, an input signal, receiving,
by the programmable gain module, a control signal, and supplying, by the programmable
gain module, at least one output current mode signal from to first current mode output
and to a second current mode output to provide a differential input signal, wherein
output of the programmable gain module is in response to the control signal. The method
also includes sensing, by an amplifier of the fully-differential programmable gain
amplifier, a common mode voltage to feed a common mode of the programmable gain module.
The method also includes producing, by a current-to-voltage of the fully-differential
programmable gain amplifier, an output signal by converting the differential input
signal, wherein the output signal is the input signal amplified based on the control
signal.
[0017] In one embodiment, the amplifier is configured as a voltage follower with the positive
input connected to a voltage ladder between the circuit paths of the amplified first
and second input signals, the negative input connected to the voltage follower's output
via a negative feedback loop, and output connected to the floating ground of the programmable
gain module.
[0018] In one embodiment, the correction module senses the common-mode signal between the
amplified first and second input signals and sends corrective feedback to the programmable
gain module.
[0019] In one embodiment, the correction module compensates for distortion caused by MOSFET
switches of the fully-differential programmable gain amplifier.
[0020] In one embodiment, the programmable gain module receives control signals to adjust
amplification of at least one signal received relative to the first input first and
second input signals.
[0021] In one embodiment, the amplifier is a voltage follower with the positive input connected
to a voltage ladder between the first current mode output and second current mode
output, the negative input connected to an output of the voltage follower by a negative
feedback loop and a floating ground supply of the programmable gain module.
[0022] In one embodiment, the amplifier is a correction module configured to sense a common-mode
signal between first current mode output and second current mode output and to provide
corrective feedback to the programmable gain module.
[0023] In one embodiment, the differential module is a fully-differential current-to-voltage
converter with a first resistive feedback loop connecting the positive output signal
path to the amplified first signal path and a second resistive feedback loop connecting
the negative output signal path to the amplified second signal path.
[0024] In one embodiment, the fully-differential programmable gain amplifier is configured
to control distortion and switching interference during amplification by sensing common
mode signal on outputs of a first current path and a second current path, comparing
common mode signal on the outputs of the first current path and a second current path
with ground, amplifying the common mode signal on the outputs of the first current
path and the second current path with the ground to produce an error signal, and applying
the resulting error signal to the programmable gain module for multiplying digital
to analog conversion.
[0025] Other aspects, features, and techniques will be apparent to one skilled in the relevant
art in view of the following detailed description of the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The features, objects, and advantages of the present disclosure will become more
apparent from the detailed description set forth below when taken in conjunction with
the drawings in which like reference characters identify correspondingly throughout
and wherein:
FIG. 1A is a circuit diagram of a prior art differential gain amplifier;
FIG. 1B is an exemplary output spectrum for a prior art differential programmable
gain amplifier having symmetrical input;
FIG. 1C is a an exemplary output spectrum for a prior art differential programmable
gain amplifier having asymmetrical input;
FIG. 2 is a graphical representation of a fully-differential programmable gain amplifier
according to one or more embodiments;
FIG. 3A is a circuit diagram of a fully-differential programmable gain amplifier according
to one or more embodiments;
FIG. 3B is an exemplary output spectrum for fully-differential programmable gain amplifier
according to one or more embodiments; and
FIG. 4 depicts operations of a fully-differential programmable gain amplifier according
to one or more embodiments.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
Overview and Terminology
[0027] One aspect of the disclosure is directed to providing a fully-differential programmable
gain amplifier with improved performance and reduced component requirements. The present
disclosure relates to fully-differential programmable gain amplifier and improved
method of reducing switching transients and interference, reducing distortion, and
extending bandwidth.
[0028] Another aspect of the disclosure is directed to providing a fully-differential programmable
gain amplifier. In one embodiment, a fully differential programmable gain amplifier
is provided that only requires the use of a dual DAC and a fully differential operational
amplifier. A further aspect is to provide a fully differential programmable gain amplifier
which does not introduce noticeable distortion in the analog output with unbalanced
input signal due to substantially different voltage drop across MOSFET switches.
[0029] A device and methods are provided for accepting two differential input voltages and
producing two differential output voltages, wherein the difference between the two
output voltages is equal to the difference between the two input voltages.
[0030] One embodiment is directed to a fully-differential programmable gain amplifier including
a programmable gain module, an amplifier coupled to the current mode outputs and a
data latch circuit of the programmable gain module, the amplifier configured to apply
common mode voltage to the data latch circuit, and a current-to-voltage converter.
According to one embodiment, the programmable gain module is configured to control
the set of switches of a resistive ladder network to provide output to the current
mode output. In one embodiment, the current-to-voltage converter is configured to
receive at least one output current mode signal and produce an output signal by converting
received differential input. Components of the fully-differential programmable gain
amplifier provide compensation of distortion caused by nonlinearity of device switches
and switch resistance.
[0031] In one embodiment, an amplifier includes common-mode rejection and digital gain control.
The amplifier also includes a first multiplying DAC configured to supply current to
a first input of a fully-differential amplifier and a second multiplying DAC configured
to supply current to a second input of the fully-differential amplifier, wherein said
first and second multiplying DACs are configured to modulate the current in said first
current path and said second current path in response to a differential input signal,
thereby producing an input differential signal defined by the difference in currents
in said first current path and said second current path. The amplifier also includes
a fully-differential current-to-voltage converter configured to produce an output
signal by converting said differential input signal.
[0032] In one embodiment a fully-differential programmable gain amplifier is configured
for providing high common mode rejection, low distortion and high rejection of switching
transients and interference. The fully-differential programmable gain amplifier can
include a first resistive R-2R ladder network with a set of single-pole double-throw
switches configured to receive a half of differential input voltage and a second resistive
R-2R ladder network with a set of single-pole double-throw switches configured to
receive a half of differential input voltage. The fully-differential programmable
gain amplifier can also include a data latch circuit configured to transfer digital
control signals to said sets of single-pole double-throw switches, and a fully-differential
current-to-voltage converter configured to receive output current mode signals provided
from said first and second resistive R-2R ladder networks through said sets of single-pole
double-throw switches. The fully-differential programmable gain amplifier can include
an additional amplifier configured to sense common-mode voltage on the inputs of said
fully-differential current-to-voltage converter, to compare common-mode voltage to
ground, to amplify the difference between common-mode voltage and ground and to feed
the common node of said data latch circuit.
[0033] In one embodiment, the fully-differential programmable gain amplifier is configured
to control distortion and switching interference during amplification by sensing common
mode signal on outputs of a first current path and a second current path, comparing
common mode signal on the outputs of the first current path and a second current path
with ground, amplifying the common mode signal on the outputs of the first current
path and the second current path with the ground to produce an error signal, and applying
the resulting error signal to the programmable gain module for multiplying digital
to analog conversion.
[0034] As used herein, a fully differential programmable gain amplifier includes plus and
minus inputs, wherein the voltage different between the plus and minus inputs is the
input differential voltage. The average of the two input voltages is the input common-mode
voltage. The fully differential programmable gain amplifier includes plus and minus
outputs. The difference between the voltages at the plus and minus outputs is the
output differential voltage. The output common mode voltage is the average of the
two output voltages and is controlled by the voltage at output common mode voltage.
[0035] According to one embodiment, amplifiers and amplifier systems discussed herein relate
to amplifier systems used in an audio system and/or for audio signals. Signals amplified
may include single ended and doubled ended input (e.g., balanced, differential, etc.).
Differential signaling and inputs may relate to signals for used in audio, data transmission,
and communication systems. Differential input may be used for high-speed data acquisition,
and can require a differential amplifier. Advantages of differential signaling can
include reduced even-order harmonics and increased dynamic range.
[0036] Another embodiment is directed to a method for fully-differential programmable gain
amplifying. In one embodiment the method includes receiving, by a programmable gain
module of a fully-differential programmable gain amplifier, an input signal, receiving,
by the programmable gain module, a control signal, and supplying, by the programmable
gain module, at least one output current mode signal from to first current mode output
and to a second current mode output to provide a differential input signal, wherein
output of the programmable gain module is in response to the control signal. The method
also includes sensing, by an amplifier of the fully-differential programmable gain
amplifier, a common mode voltage to feed a common mode of the programmable gain module.
The method also includes producing, by a current-to-voltage of the fully-differential
programmable gain amplifier, an output signal by converting the differential input
signal, wherein the output signal is the input signal amplified based on the control
signal.
[0037] Another embodiment is directed to processes for controlling distortion and switching
interference during amplification, said method comprising steps of sensing the common
mode signal on the outputs of a first current path and a second current path, comparing
the common mode signal on the outputs of a first current path and a second current
path with the ground, amplifying the common mode signal on the outputs of a first
current path and a second current path with the ground to produce an error signal,
and applying the resulting error signal to digital control signal for multiplying
DACs.
[0038] As used herein, the terms "a" or "an" shall mean one or more than one. The term "plurality"
shall mean two or more than two. The term "another" is defined as a second or more.
The terms "including" and/or "having" are open ended (e.g., comprising). The term
"or" as used herein is to be interpreted as inclusive or meaning any one or any combination.
Therefore, "A, B or C" means "any of the following: A; B; C; A and B; A and C; B and
C; A, B and C". An exception to this definition will occur only when a combination
of elements, functions, steps or acts are in some way inherently mutually exclusive.
[0039] Reference throughout this document to "one embodiment," "certain embodiments," "an
embodiment," or similar term means that a particular feature, structure, or characteristic
described in connection with the embodiment is included in at least one embodiment.
Thus, the appearances of such phrases in various places throughout this specification
are not necessarily all referring to the same embodiment. Furthermore, the particular
features, structures, or characteristics may be combined in any suitable manner on
one or more embodiments without limitation.
Exemplary Embodiments
[0040] Referring now to the figures, FIG. 2 depicts a graphical representation of a fully-differential
programmable gain amplifier according to one or more embodiments. FIG. 2 is shown
as a block diagram for components of a fully-differential programmable gain amplifier
200. According to one embodiment, fully-differential programmable gain amplifier
200 includes one or more components configured to reduce switching transients and interference,
reduce distortion and extending bandwidth. As will be discussed in more detail with
respect to FIG. 3A, a circuit arrangement may be provided for the components of the
fully-differential programmable gain amplifier
200. Fully-differential programmable gain amplifier
200 may be used in an audio system. Accordingly, fully-differential programmable gain
amplifier
200 maybe configured to amplify audio signals, including balanced and single ended input
audio signals.
[0041] According to one embodiment, fully-differential programmable gain amplifier
200 includes a first input
205, a second input
206, programmable gain module
210, differential module
215 and correction module
225, first output
220 and second output
221.
[0042] First input
205 and second input
206 relate to the input of fully-differential programmable gain amplifier
200, wherein the input signal received at first input
205 and second input
206 may be amplified. According to one embodiment, first input
205 and second input
206 may be configured to receive differential input. In certain embodiments, signals
received may relate to balanced or single ended inputs. Balanced inputs may be based
on voltage between two individual inputs, such as first input
205 and second input
206 may, within a common mode range. A balanced input may have signals with an opposite
polarity. By way of example, a balanced input (e.g., differential signal input) may
be provided by inputs carrying signals of opposite polarity to each other (e.g., TRS
and XLR connectors, etc.). In certain embodiments, an input of fully-differential
programmable gain amplifier
200 received a single ended input relates to a source providing voltage between the input
channel high and low level ground common to all the inputs.
[0043] Programmable gain module
210 is configured to supply at least one output current mode signal to provide a differential
input signal for differential module
215 of fully-differential programmable gain amplifier
200. In one embodiment, programmable gain module
210 is configured to receive input for fully-differential programmable gain amplifier
200 from first input
205 and second input
206. Accordingly, programmable gain module
210 may be coupled to first input
205 and second input
206.
[0044] According to one embodiment, programmable gain module
210 may include a data latch circuit configured to control a set of switches for first
input
205 (e.g., first set of switches) and a second set of switches for second input
206 (e.g., second set of switches). As will be discussed in more detail with respect
to FIG. 3A, programmable gain module
210 may include first resistive ladder network to provide output to the first current
mode output and a second resistive ladder network to provide output to a second current
mode output, and control the second set of switches for the first resistive ladder
network to provide output to the second current mode output. Gain adjustment of an
amplifier
200 can be accomplished by connecting a resistance ladder (R-2R) digital-to-analog converter
(i.e. multiplying DAC) as a programmable gain element to the amplifier input, such
as first input
205 and second input
206. When placed in a feedback loop the multiplying DAC of programmable gain module
210 permits adjustment of the feedback current, and thus gain, for the amplifier by allowing
adjustment for the impedance of the circuit. In one embodiment, the multiplying DAC
of programmable gain module
210 is placed in the negative feedback loop. According to one embodiment, programmable
gain module
210 may include two complementary multiplying digital to analog converters (DAC). With
conventional arrangements including two multiplying DACs, problems may be presented
maintaining common-mode rejection and low interference from digital control signals.
Embodiments allow for amplifier
200 to recover the differential signal while also maintaining common-mode rejection and
low interference from digital control signals.
[0045] Output
211 of programmable gain module
210 may include a first common mode output and a second common mode output. Output
211 of programmable gain module
210 may be based on first current mode output and second current mode output circuit
paths of the amplified first and second input signals received from first input
205 and second input
206, respectively.
[0046] Common-mode voltage is the voltage signal in common between the two inputs of differential
module
215. Principles of the disclosure, including the components and arrangement of components
of amplifier
200 provide a high common-mode rejection ratio to keep the common-mode voltage from affecting
the output voltage.
[0047] According to one embodiment, the programmable gain module
210 receives a control signal
230 to control amplification. In certain embodiments, gain module
210 receives a control signal
230 directly. In other embodiments, gain module
210 receives a control signal
230 by way of isolation module
235, which may be optional. Isolation module
235 may include a galvanic isolator to block low voltage DC current. Isolation module
235 may be configured to transfer digital control signals to a data latch circuit programmable
gain module
210; as such the control signals may pass through an isolation module.
[0048] According to one embodiment, the programmable gain module
210 uses a floating power source as its reference voltage.
[0049] According to one embodiment, correction module
225 is coupled to the current mode outputs of programmable gain module
210. Correction module
225 may include an amplifier configured to apply common mode voltage to a data latch
circuit of programmable gain module
210. Correction module
225 provides feedback to programmable gain module
210.
[0050] Output
211 of programmable gain module
210 may be received by differential module
215. According to one embodiment, differential module
215 may include a current-to-voltage converter coupled to output
211, such as first current mode output and the second current mode output. Differential
module
215 may produce an output signal by converting differential input received from the at
least one output current mode signal from the first current mode output and the second
current mode output. Output of differential module
215 may be a differential output to first output
220 and second output
221. In one embodiment, differential module
215 may provide the positive and negative output signals to other devices by way of first
output
220 and second output
221.
[0051] FIG. 3A is a circuit diagram of a fully-differential programmable gain amplifier
according to one or more embodiments. According to one embodiment, fully-differential
programmable gain amplifier
300 may be configured to operate with differential inputs and differential outputs. According
to another embodiment, fully-differential programmable gain amplifier
300 is configured to reducing switching transients and interference, reducing distortion
and extending bandwidth.
[0052] According to one embodiment, fully-differential programmable gain amplifier
300 includes a first input
301, a second input
302, first output
303, second output
304, programmable gain module
310, correction module
320, and differential module
330.
[0053] According to one embodiment, first input
301 and second input
302 may be configured to receive an input signal to be amplified. In one embodiment,
first input
301 and second input
302 may be configured to receive a differential input. In another embodiment, first input
301 and second input
302 may be configured to receive a balanced input. According to another embodiment, first
input
301 and second input
302 may be configured to receive a single ended input. Differential signals may be less
sensitive to external disturbances like small voltage differences between grounds
and thus, advantageous for route the signal to another circuit (which might be on
a different ground) while keeping the signal noise and disturbance free. Fully-differential
programmable gain amplifier
300 can provide a single ended signal anyway by using one output of the amplifier.
[0054] Programmable gain module
310 is coupled to first input
301 and second input
302 and configured to receive input signals. According to one embodiment, input signals
received form first input
301 are routed to a first current path of programmable gain module
310 and input signals received form second input
302 are routed to a second current path of programmable gain module
310. According to one embodiment, operation of fully-differential programmable gain amplifier
300 to control gain (e.g., amplification) of signals received at first input
301 and second input
302, may be controlled by a control signal received by input
305.
[0055] According to one embodiment, programmable gain amplifier
310 includes a dual multiplying DAC configuration including a first resistance (R-2R)
ladder network
311, a second resistance (R-2R) ladder network
315, first set of single-pole double-throw switches
3121-n, a second set of single-pole double-throw switches
3141-n and data latch circuit
313 (e.g., data latches). According to one embodiment, first resistance (R-2R) ladder
network
311 and second resistance (R-2R) ladder network
315 each are formed from an electrical circuit made from repeating units of resistors.
First resistance (R-2R) ladder network 311 and second resistance (R-2R) ladder network
315 may be formed by one of a string resistor ladder and an R-2R ladder. An R-2R Ladder
configuration may provide a simple and inexpensive way to perform digital-to-analog
conversion, where the repetitive arrangements of precise resistor networks in a ladder-like
configuration. A string resistor ladder configuration may implement a non-repetitive
reference network.
[0056] Gain adjustment of fully-differential programmable gain amplifier
300 can be accomplished by connecting a resistance ladder (R-2R), such as first resistance
(R-2R) ladder network
311 or second resistance (R-2R) ladder network
315, to digital-to-analog converter (i.e. multiplying DAC) of programmable gain amplifier
300 as a programmable gain element to the amplifier's input or inputs. When placed in
the feedback loop, the multiplying DAC of programmable gain amplifier
300 permits adjustment of the feedback current, and therefore gain, for the fully-differential
programmable gain amplifier
300 by allowing adjustment for the impedance of the circuit. The multiplying DAC may
be placed in the negative feedback loop of the fully-differential programmable gain
amplifier
300.
[0057] Galvanic isolator
316 transfers digital control signals from input
305 to data latch circuit
313, separating stray electrical currents from the main circuit to reduce interference
from digital control signals. Galvanic isolator
316 may receive an input signal ranging from 0-5 volts or 0 to the Vcc (supply voltage).
Output of the amplifier may be on the order to -208 to +208 volts.
[0058] Data latch circuit
313 provides digital control of electronic switches
3121-n and
3141-n. According to one embodiment, a data latch circuit
313 is configured to control a first set of switches, such as switches
3121-n, for the first resistive ladder network to provide output to the first current mode
output, and control a second set of switches
3141-n for the second resistive ladder network to provide output to the second current mode
output.
[0059] An important advantage of this configuration of fully-differential programmable gain
amplifier
300 is minimization of transients for electronic switches
3121-n and
3141-n when changing their position between nodes with the same potential - ground and virtual
ground (inputs of the current-to-voltage converters). Another advantage is mutual
compensation of interference from switch control digital signals provided by differential
module
330. In addition the configuration of fully-differential programmable gain amplifier
300 does not require a high number of components and high tolerances.
[0060] According to one embodiment, an input signal of programmable gain amplifier
300 includes is differential input to first input
301 (e.g., (INPUTA) and second input
302 (e.g., INPUTB). The positive input current from first input
301 (e.g., (INPUTA) is steered by switches
3121-n to a first current mode output
312 which is coupled to a first input of the fully-differential current-to-voltage converter
330, or to a floating low impedance current sink. The negative input current from second
input
302 (e.g., INPUTB is steered by switches
3141-n to a second current mode output
316 which is coupled to a second input of the fully-differential current-to-voltage converter
330 or to a floating low impedance current sink. Fully-differential current-to-voltage
converter
330 translates the portion of the input currents remaining after passing through dual
multiplying DAC of programmable gain module
310 into a differential voltage signal.
[0061] According to one embodiment, correction module
320 includes an amplifier
321 coupled to the first current mode output
312, the second current mode output
316, and the data latch circuit
313. Amplifier
321 is configured to apply common mode voltage to the data latch circuit
313.
[0062] According to one embodiment, correction module
320 includes amplifier
321 as a voltage follower to sense the common mode voltage on the inputs of fully-differential
current-to-voltage converter
330 and applies the common mode voltage to a digital control signal for multiplying DAC
of programmable gain module
310. Voltage follower
321 of correction module
320 also provides a low-impedance current sink for the DAC resistive (R-2R) ladders programmable
gain module
310. Correction module
320 provides a high common-mode rejection ratio that is desirable to keep the common-mode
voltage from affecting the output voltage.
[0063] Floating supply
317 provides power for data latch circuit
313. Programmable gain module
310 includes floating ground from floating supply
317 and feedback from correction module
320 to adjust a voltage level of the floating ground. Programmable gain module
310 includes may use floating power supply
317 (e.g., floating power source) source as a reference voltage. According to one embodiment,
floating power supply
317 prevents distortion, and can allow for matching source.
[0064] According to one embodiment, differential module
330 includes a current-to-voltage converter
331 coupled to the first current mode output
312, the second current mode output
316, first output
303 and second output
304. According to one embodiment, current-to-voltage converter
331 is configured to receive at least one output current mode signal from the first current
mode output and the second current mode output, and produce an output signal by converting
differential input received from the at least one output current mode signal from
the first current mode output and the second current mode output.
[0065] A noninverting input of current-to-voltage converter
331 is connected with the inverting output, first output
303 (e.g., OUTPUTA) through resistor
332 (e.g., in series). According to one embodiment, resistor
332 can set the maximum gain of differential module
330. The inverting input current-to-voltage converter
331 is connected with the noninverting output, second output
304 (e.g., OUTPUTB) through a series resistor
333. According to one embodiment, resistor
333 can set the maximum gain of differential module
330. According to another embodiment, resistor
332 and resistor
332 may have the same resistance (e.g., matched). The output of fully-differential programmable
gain amplifier
300 appears between first output
303 and second output
304.
[0066] The noninverting and inverting inputs of current-to-voltage converter
331 may both be connected to the input of the amplifier
321 through resistors
322 and
323 respectively. According to one embodiment, resistor
322 and resistor
323 may have the same resistance (e.g., matched). Because of the high open loop gain
of voltage follower
321 the voltage between inputs of fully-differential current-to-voltage converter
331 is negligibly low. The output of amplifier
321 is equal to a fraction of the sum of the voltages on the input terminals of first
input
301 (e.g., (INPUTA) and second input
302 (e.g., INPUTB). The voltage at the positive input
324 of voltage follower
321 (e.g., follower) may be equal to the average of the voltages on inputs of fully-differential
current-to-voltage converter
331. The output of voltage follower
321 may be configured to be equal to or roughly equal to the positive input of fully-differential
current-to-voltage converter
331. When the input voltages have the same amplitude but opposite sign the output of voltage
follower
321 is equal to zero. The output voltage of the voltage follower
321 with the floating voltage source
317 feeds the data latch circuitry
313. Floating power supply
317 and voltage follower
321 power data latches
313 and thus, can shift control signals up and down, such as control signals for programmable
gain amplifier
300 provided by input
305.
[0067] Floating power supply
317 may relate to the same power source for data latches
313. In contrast to connection of a minus terminal of floating power supply
317, the minus terminal of floating power supply
317 is coupled to data latches
313 and output of voltage follower
321. The output voltage follower
321 may be small, but an important addition to floating power supply
317. According to one embodiment, voltage follower
321 senses a common mode signal at the two inputs of current-to-voltage converter
331 and floats the latches of data latch circuit
313 on both sides, and floats what would be the ground signal.
[0068] The output voltage of voltage follower
321 also can provide balanced feedback to control voltage input to differential module
330. The output voltage of amplifier
321 also shifts the level of control signals of switches
3121-n and
3141-n by the average of the voltage on the
331 inputs and provides partial obtained from the data latch circuitry
313 and provides partial compensation of distortion associated with MOSFET switches nonlinearity.
As such, fully-differential programmable gain amplifier
300 compensates for distortion caused by nonlinearity of MOSFET switches. Resistance
of closed MOSFET switch is a function of applied voltage. Full distortion compensation
takes place when the signals on first input
301 (e.g., (INPUTA) and second input
302 (e.g., INPUTB) have equal amplitude and opposite phase.
[0069] The output currents of programmable gain module
310 are steering in the inverting and noninverting inputs of fully-differential current-to-voltage
converter
331. Noninverting input of fully-differential current-to-voltage converter
331is connected with the inverting output through a series resistor
332, inverting input of fully-differential current-to-voltage converter
331is connected with the noninverting output through a series resistor
333. The fully differential programmable gain amplifier output appears between first output
303 (e.g., OUTPUTA) and second output
304 (e.g., OUTPUTB).
[0070] Noninverting and inverting inputs of fully-differential current-to-voltage converter
331 are connected to the input of the voltage follower
321 with resistors
322, 323. Because of the high open loop gain the voltage between inputs of fully-differential
current-to-voltage converter
331 is negligibly low. The output of the voltage follower
321 is equal to the fraction of the sum of the voltages on the first input
301 (e.g., (INPUTA) and second input
302 (e.g., INPUTB). When the input voltages on first input
301 (e.g., (INPUTA) and second input
302 (e.g., INPUTB) have the same amplitude but opposite sign, the output of voltage follower
321 is equal to zero. The output voltage of voltage follower
321 with the floating power supply
317 feed the data latch circuitry. The output voltage follower
321 modulates the switch control signals obtained from the data latch circuitry of data
latches
313 and provides partial compensation of distortion associated with MOSFET switch nonlinearity
as shown in FIG. 3B.
[0071] Referring now to FIG. 3B, an exemplary output spectrum
350 is shown for differential programmable gain amplifier
300 with asymmetrical drive. For example, an input signal having a pure 1kHz sine wave,
with the input signal applied to a single input terminal or input
301 and second input signal terminal
302 shorted to ground, will generate output spectrum
350 having peak
355 and second order distortion shown by peak
356. Differential programmable gain amplifier
300 compensates for second order distortion. By way of example, peak 356 represents partial
compensation of distortion associated with MOSFET switch nonlinearity.
[0072] Benefits of fully-differential programmable gain amplifier
300 can include reducing the number of operational amplifiers (e.g., 1 amplifier of differential
module
330 compared to 4 amplifiers of FIG. 1A). In addition, matching of amplifiers is not
required.
[0073] FIG. 4 depicts operations of a fully-differential programmable gain amplifier according
to one or more embodiments. Process
400 shows operations of a fully-differential programmable gain amplifier, such as fully-differential
programmable gain amplifier
200 of FIG. 2, and fully-differential programmable gain amplifier
300 of FIG. 3. Operations of process
400 may be performed by one or more components of a fully-differential programmable gain
amplifier. Process
400 may be performed to control distortion and switching interference during amplification.
[0074] Process
400 includes receiving input at block
405 and receiving a control signal, such as a gain control input, at block
410. According to one embodiment, input received at block
405 relates to an input signal, such as a differential input signal or single ended signal
received. Process
400 may be employed to control the amplification of the signal and or signals received
at block
405 based on a gain control signal received at block
410. According to one embodiment, gain control signals may be DC signals. Process
400 may optionally include isolate the gain control input from an amplifier at block
411. Isolation at block
410 may be performed by a galvanic isolator of the fully-differential programmable gain
amplifier.
[0075] At block
415, process
400 can include applying a signal gain to received input. Block 414 may be performed
by a programmable gain unit of the fully-differential programmable gain amplifier.
Based on a first and second input signal detected by the programmable gain unit and
amplified at block
415, wherein the signal is amplified based on a gain control signal received at block
410. Converting at block
415 may include accepting feedback from a correction module, such as feedback generated
at block
420.
[0076] As a result of applying a signal gain at block
415, process
400 can supply at least one output current mode signal from to first current mode output
and to a second current mode output to provide a differential input signal. Output
of the programmable gain module at block
415 may be in response to and controllable by a control signal received by the fully-differential
programmable gain amplifier.
[0077] At block
420, process
400 can include detecting a common-mode signal. Process
400 may be performed to control distortion and switching interference during amplification.
Block
420 may include sensing the common mode signal on the outputs of a first current path
and a second current path of a programmable gain element (e.g., programmable gain
element
310), and comparing the common mode signal on the outputs of a first current path and
a second current path with the ground. An amplifier (e.g., amplifier
321) of the fully-differential programmable gain amplifier can sense a common mode voltage
to feed a common mode of the programmable gain module. The common mode signal on the
outputs of a first current path and a second current path (e.g., first current mode
output
312, the second current mode output
316) with the ground may be amplified to produce an error signal at block
420. The resulting error signal may be applied (e.g., see output path of block
420) as a digital control signal for multiplying DACs of the programmable gain element
at block
415. In that fashion, feedback may be provided by a correction module to the programmable
gain module by sensing signal errors from the amplified first and second input signal.
[0078] Operations at blocks
415 and
420 may be performed to control differential input to a differential module. Operations
at block
415 can include a programmable gain module receiving control signals to adjust amplification
of at least one signal received relative to the first input first and second input
signals. An amplifier of a correction module coupled to the programmable gain module,
may be configured to sense a common-mode signal between first current mode output
and second current mode output and to provide corrective feedback to the programmable
gain module at block
420. The amplifier may be configured as a voltage follower with the positive input connected
to a voltage ladder between the circuit paths of the amplified first and second input
signals, the negative input connected to the voltage follower's output via a negative
feedback loop, and output connected to the floating ground of the programmable gain
module. The correction module can sense the common-mode signal between the amplified
first and second input signals and send corrective feedback to the programmable gain
module. As such the correction module compensates for distortion caused by MOSFET
switches of the fully-differential programmable gain amplifier. The amplifier amplifies
the common mode signal on the outputs of the first current path and the second current
path with the ground to produce an error signal at block
420. The error signal is supplied to the programmable gain module for multiplying digital
to analog conversion at block
415.
[0079] At block
425, process
400 can include generating a differential voltage. By way of example, a differential
module (such as differential module
330 including a current-to-voltage converter
331) produces a positive and a negative output signal. The output signals are opposite
to each other and equal in magnitude to the difference between the amplified first
and second input signals. The output signals at block
425 can include differential output. The output signals at block
425 can include converting the differential input signal to output an amplified input
signal based on the control signal. Operations at block
425 may be performed by a differential module including a fully-differential current-to-voltage
converter with a first resistive feedback loop connecting the positive output signal
path to the amplified first signal path and a second resistive feedback loop connecting
the negative output signal path to the amplified second signal path. The fully-differential
programmable gain amplifier is configured to control distortion and switching interference
during amplification.
[0080] While this disclosure has been particularly shown and described with references to
exemplary embodiments thereof, it will be understood by those skilled in the art that
various changes in form and details may be made therein without departing from the
scope of the claimed embodiments.
1. A fully-differential programmable gain amplifier comprising:
a first input;
a second input;
a first output;
a second output;
a programmable gain module coupled to the first input and the second input, the programmable
gain module including
a data latch circuit configured to
control the first set of switches for the first resistive ladder network to provide
output to the first current mode output, and
control the second set of switches for the first resistive ladder network to provide
output to the second current mode output;
an amplifier coupled to the first current mode output, the second current mode output,
and the data latch circuit, the amplifier configured to apply common mode voltage
to the data latch circuit; and
a current-to-voltage converter coupled to the first current mode output, the second
current mode output, the first output and the second output, the current-to-voltage
converter configured to
receive at least one output current mode signal from the first current mode output
and the second current mode output, and
produce an output signal by converting differential input received from the at least
one output current mode signal from the first current mode output and the second current
mode output.
2. The fully-differential programmable gain amplifier of claim 1, wherein the programmable
gain module is a dual multiplying digital to analog converter.
3. The fully-differential programmable gain amplifier of claim 1, wherein the programmable
gain module includes
a first resistive ladder network coupled to the first input,
a first set of switches for the first resistive ladder network, the first set of switches
coupled to a first current mode output,
a second resistive ladder network coupled to the second input, and
a second set of switches for the first second ladder network, the second set of switches
coupled to a second current mode output,
the data latch circuit configured to control the first set of switches for the first
resistive ladder network to provide output to the first current mode output, and control
the second set of switches for the first resistive ladder network to provide output
to the second current mode output.
4. The fully-differential programmable gain amplifier of claim 1, wherein the programmable
gain module receives control signals to adjust amplification of at least one signal
received relative to the first input first and second input signals.
5. The fully-differential programmable gain amplifier of claim 1, wherein the amplifier
is a voltage follower with the positive input connected to a voltage ladder between
the first current mode output and second current mode output, the negative input connected
to an output of the voltage follower by a negative feedback loop and a floating ground
supply of the programmable gain module.
6. The fully-differential programmable gain amplifier of claim 1, wherein the amplifier
is a correction module configured to sense a common-mode signal between first current
mode output and second current mode output and to provide corrective feedback to the
programmable gain module.
7. The fully-differential programmable gain amplifier of claim 1, wherein the current-to-voltage
converter is differential module configured to produce a positive output signal to
the first output and a negative output signal to the second output, wherein the first
output and second output are opposite each other and equal in magnitude to the difference
between the amplified first and second input signals.
8. The fully-differential programmable gain amplifier of claim 1, wherein the current-to-voltage
converter includes a first output feedback loop coupled to the first output and an
input of the current-to-voltage converter, and a second output feedback loop coupled
to the first output and an input of the current-to-voltage converter.
9. The fully-differential programmable gain amplifier of claim 1, further comprising:
a floating supply to power the programmable gain module; and
a galvanic isolator coupled to the programmable gain module, the galvanic isolator
configured to block low voltage DC current to the programmable gain module.
10. A fully-differential programmable gain amplifier comprising:
a first input;
a second input;
a first output;
a second output;
a programmable gain module coupled to the first input and the second input, the programmable
gain module including
a first resistive ladder network coupled to the first input,
a first set of switches for the first resistive ladder network, the first set of switches
coupled to a first current mode output,
a second resistive ladder network coupled to the second input,
a second set of switches for the first second ladder network, the second set of switches
coupled to a second current mode output,
a data latch circuit configured to
control the first set of switches for the first resistive ladder network to provide
output to the first current mode output, and
control the second set of switches for the first resistive ladder network to provide
output to the second current mode output;
an amplifier coupled to the first current mode output, the second current mode output,
and the data latch circuit, the amplifier configured to apply common mode voltage
to the data latch circuit; and
a current-to-voltage converter coupled to the first current mode output, the second
current mode output, the first output and the second output, the current-to-voltage
converter configured to
receive at least one output current mode signal from the first current mode output
and the second current mode output, and
produce an output signal by converting differential input received from the at least
one output current mode signal from the first current mode output and the second current
mode output.
11. A method for fully-differential programmable gain amplifying, the method comprising:
receiving, by a programmable gain module of a fully-differential programmable gain
amplifier, an input signal;
receiving, by the programmable gain module, a control signal;
supplying, by the programmable gain module, at least one output current mode signal
from to first current mode output and to a second current mode output to provide a
differential input signal, wherein output of the programmable gain module is in response
to the control signal;
sensing, by an amplifier of the a fully-differential programmable gain amplifier,
a common mode voltage to feed a common mode of the programmable gain module; and
producing, by a current-to-voltage of the fully-differential programmable gain amplifier,
an output signal by converting the differential input signal, wherein the output signal
is the input signal amplified based on the control signal.
12. The method of claim 11, wherein the amplifier is configured as a voltage follower
with the positive input connected to a voltage ladder between the circuit paths of
the amplified first and second input signals, the negative input connected to the
voltage follower's output via a negative feedback loop, and output connected to the
floating ground of the programmable gain module.
13. The method of claim 11, wherein the correction module senses the common-mode signal
between the amplified first and second input signals and sends corrective feedback
to the programmable gain module.
14. The method of claim 11, wherein the correction module compensates for distortion caused
by MOSFET switches of the fully-differential programmable gain amplifier.
15. The method of claim 11, wherein the fully-differential programmable gain amplifier
is configured to control distortion and switching interference during amplification
by
sensing common mode signal on outputs of a first current path and a second current
path,
comparing common mode signal on the outputs of the first current path and a second
current path with ground,
amplifying the common mode signal on the outputs of the first current path and the
second current path with the ground to produce an error signal, and
applying the resulting error signal to the programmable gain module for multiplying
digital to analog conversion.